Many devices such as power tongs employ a transmission or gear train having different gears (or sets of gears) for operating at different speeds and torque ratios. An example of such a power tong is seen in U.S. Pat. No. 4,631,987, which is incorporated by reference herein in its entirety. In order to run the gear train at different speeds, the power source (e.g., a motor shaft) must selectively engage the different gears in the gear train. This typically entails selectively bringing a drive gear on the motor shaft into engagement with the appropriate set of gears in the gear train in order to run the device at the desired speed.
Transmissions in power tongs are normally less complex than in other machinery such as automobiles. Typical manual automobile transmissions have mechanisms such as a clutch to selectively remove load from the gears and synchronizers to assist the gears in meshing at the same speed. With these mechanisms to assist gear meshing, the shape of the top surface of the gears is not of great consequence and is normally flat.
However, because power tongs do not have complex gear meshing mechanisms and because the gears of the transmission may be stationary when the shift occurs, the largely flat top surface on the teeth of such gears often interferes with the gears meshing smoothly. Operators will typically attempt to run the motor at low speeds to facilitate the meshing of the gears. However, this often leads to the “grinding” of the gears and excessive wear on the gear teeth, particularly if the motor is run at too high of a speed during meshing. It would be a significant improvement in the art to provide a gear system which facilitated meshing in general and in certain examples, facilitated meshing without applying power to the drive gear.